Process for manufacturing brass and bronze alloys containing lead



Aug. 13, 1957 ea/ Confenf) lead Cora Ile/fz w. BUNGARDT 2,802,733

PROCESS FOR MANUFACTURING BRASS AND BRQNZE ALLoys CONTAINING LEAD FiledJune 22, 1955 iii:

illll IIJ Bod /'ame/@r (mm/J ill ll|1| United States Patent Yi() PROCESSF OR MANUFACTURING BRASS AND BRONZE ALLOYS CGNTAINING LEAD WalterBungardt, Essen, Germany, assignor to Th. Goldschmidt A. G., Essen,Germany, a company of Germany Application .lune 22, 1955, Serial No.517,155 Claims priority, application Germany July 9, 1954 Claims. (Cl.7S-156.5)

This invention relates to process for manufacturing brass and bronzealloys containing lead; and it comprises an improvement in themanufacture of castings from bronze and brass alloys containing over 50%of copper wherein a small amount of misch metal, amounting to from about.2 to 5% by weight, is added to the alloy before casting, whereby thecastability of the alloy is improved and a casting is produced havingimproved microcrystalline structure and uniformity of composition. Theinvention also includes the improved castings produced by the describedprocess. An important feature of the invention is the improvement inleaded brasses and bronzes produced by the described addition of mischmetal, these alloys containing from about l to 35% lead and producingcastings whose surfaces are free from inclusions of lead; all as morefully hereinafter set forth and as claimed.

While the casting of brass and bronze alloys has been perfected to anextent not achieved with most other alloys, it is also true that theproperties of most of these alloys leaves considerable room forimprovement. This is especially true in the casting of intricate partswhere the molten alloys lack suliicient fluidity to flow into smallrecesses and cavities, In many cases the castings formed are notentirely uniform in composition and the microcrystalline structures aresometimes not uniform throughout and are difficult to reproduce.Moreover special difficulties are encountered with certain types ofbrass and bronze alloys.

For example in the case of alloys classilied as leaded brasses andbronzes of the type widely used as bearing metals diliicultiesfrequently arise due to inclusions of lead in the surfaces of thecastings. These inclusions appear to be caused by lead oozing to thesurface during the solidilication of the castings. A pitted surfaceresults which must be machined before use. The turnings can, l

of course, be recovered and included in the next alloy batch in order toreduce the loss of metal but the machined castings contain less leadthan desired. Moreover this lead content is unequally distributed sincethe surface layers contain more lead than the interiors of the castings.

I have discovered that the above described difiiculties can besubstantially eliminated by including from about .2 to 5% of misch metalin these brass and bronze alloys. Misch metal is a well known rare earthmetal or cerum alloy and is sold under that name. It contains from about45 to 55% of cerium, 25 to 35% of lanthanum, approximately to 18%neodymium, with a balance of yttria and some further incidentalimpurities such as iron, silicon, carbon, phosphorous, aluminium,calcium, manganese and magnesium usually totalling less than 2.5%. Insome impure misch metals the iron content may amount to 2% or slightlyabove. While these can be used in the present invention I prefer to usepure misch metals in which the iron content does not exceed 1% byweight.

My tests show that all the alloys classified as leaded brasses andbronzes can be substantially improved by incorporating small amounts ofmisch metal in their castings. These alloys are included within the A.S. T. M. designation: B 119-45, namely: leaded red brass containing 2 to8% zinc, tin less than 6%, usually less than the zinc, and lead over0.5%; leaded semi-red brass containing 8 to 17% zinc, tin less than 6%and lead over 0.5%; leaded yellow brass containing over 17% zinc, tinless than 6%, under 2% total aluminum, manganese, nickel, or iron andlead over 0.5%; leaded high-strength yellow brass (leaded manganesebronze) containing over 17% zinc, tin less than 6%, over 2% total ofaluminum, mauganese, tin, nickel, and iron and over 0.5% lead; leadednickel brass (leaded nickel silver) containing over 10% zinc, nickel inamounts suliicient to give white color and lead over 0.5%; leaded tinbronze containing up to 20% tin, zinc less than tin, lead over 0.5% andless than 6%; high-leaded tin bronze containing up to 20% tin, zinc lessthan tin, lead over 6%; lead bronze containing over lead, zinc less thantin, tin under 10%; and leaded nickel bronze containing over 10% nickel,zinc less than nickel, under 10% tin and over 0.5% lead. Thecastability, machinability and uniformity of composition of all thesealloys are improved by the addition of misch metal in accordance withthis invention.

My improved leaded bronzes contain from about 1 to of lead, from about 3to 10% of tin, from about 0 to 4.5% of zinc, from about 0 to 3% ofnickel and from about .2 to 5.0% (preferably from about 0.2 to 0.5%) ofcerium misch metal, with a balance, over of copper.

The accompanying drawing shows the striking improvement in theuniformity of composition produced in castings of a typical leadedbronze rod, containing 15% lead, 3% tin, 2.5% nickel and 79.5% copper,by the addition to this alloy of only 0.3% misch metal. The data shownplotted in the three figures of the drawing were obtained by castingrods in sand at different casting temperatures from the alloy stated,both with and without the addition of 0.3% misch metal, all of the rodshaving original diameters of 35 mm., then machining ofi surface layersfrom these rods to depths of 0.25 mm., 0.75 mm., 1.25 mm., 1.75 mm. etc.and analyzing the cuttings for their lead content. The lead contentsthus obtained are plotted in the figures as ordinates against the roddiameters (after machining) as abscissas.

The rod diameters are plotted in such fashion that the centers of thecoordinates coincide with the surfaces of the rods, i. e. at diametersof 35 mm. The curves thus show the lead contents of the rods as afunction of the distances from the surface layer. The dotted lines ineach of the figures represent the data obtained with alloys free frommisch metal while the full lines are plotted from the data obtained withthe same alloys but containing 0.3% added misch metal.

The two alloy compositions used in the three figures were the same andthe procedures used in obtaining the data were identical except for thetemperatures used in producing the castings. The data plotted in Fig. 1were obtained from castings produced at a casting temperature of 1100"C., those plotted in Fig. 2 were obtained from castings cast at atemperature of i200" C., while those plotted in Fig. 3 were fromcastings produced at 1300a C. Thus the figures show the effect of thecasting temperature on the uniformity of the alloy compositions as afunction of the distance from the surface layer.

The figures of the drawing show that in castings free from misch metalthere is a surprisingly high concentration of lead in the surfacelayers, ranging from 35.2% to 84.9%. They also show that when mischmetal is added to the alloys the lead distribution becomes substantiallyuniform throughout the castings although Figs. 1 and 2 show that at thelower casting temperatures the concentration of lead in the surfacelayer is slightly below the average rather than above. There is anoptimum percentage of misch metal for each casting temperature at whichthe surface concentration of lead becomes substantially identical tothat of the average. In Fig. 3 the percentage is close to this optimumwhereas in Figs. 1 and 2 the percentage of misch metal is slightly abovethe optimum for the casting temperatures employed. In most cases theaddition of only from about 0.2 to 0.5% of cerium misch metal or fromabout 0.1 to 0.3%, based on its cerium content, is required to producebest results.

All of the sand castings produced in the above described tests from thealloy which was free from misch metal were found to have uneven andpitted surfaces rich in lead. Before commercial use these surfaces wouldhave had to be removed resulting in considerable costs both formachining and for metal recovery. In contrast the castings produced fromthe alloy containing misch metal were copper-colored, smooth andhomogeneous and would have required a minimum of finishing before use.

The various extraneous metals and impurities present in technical gradesof misch metal generally produce no detrimental elfects. The noveltechnical effect, namely the elimination of surface inclusions of lead,is obtained regardless of these impurities. The other physical andmechanical properties, such as hardness, malleability and elasticity areeither maintained or improved by the misch metal additions regardless ofimpurities present in the misch metal. However in the case of severalspecial uses for the alloys in question it is desirable to employ thepurer grades of misch metal in order to keep the impurities, especiallyiron, to a minimum.

The misch metal can be added as such to the molten copper base alloy orin the form of a cerium-rich prealloy, if desired. My alloys areparticularly suitable for use as bearing metals, for armatures andapparatus for the chemical and electrical industries.

While I have emphasized in the foregoing the elimination of leadinclusions, i. e. the segregation of lead, as being an important newtechnical effect obtained by the addition of misch metal to leadedbrasses and bronzes, an etect which is of equal importance in many casesis the elimination of microporosity in and improvement of the structureof castings. Thus I have found that leaded copper base alloys can beimproved which have the following specic compositions:

5% tin, 5% lead, 5% zinc, balance copper 4% tin, 6% lead, 7% zinc,balance copper 3% tin, 7% lead, 9% zinc, balance copper 3% tin, 5% lead,16% zinc, 16% nickel, balance copper By the addition of from about 0.2to 0.5% misch metal these alloys show improved castability, animprovement in structure, greater uniformity in technical properties andelimination of microporosity.

Malleable copper alloys of the type classied as brass and special brassalloys can also be improved by the addition of from about .2 to 3% ofmisch metal. The improved alloys show greater formability both whenheated and in the cold, when rolled into sheet, when forged, whenextruded and when drawn, for example.

The so-called gun metals, containing tin and 2% zinc or 8% tin and 4%zinc, with a balance of copper, can be improved by similar additions ofmisch metal. The castability of these gun metals is improved and thecastings have a greater uniformity.

The properties of the so-called aluminum bronzes can also be improved bythe addition of small amounts of misch metal. These alloys contain fromabout 88 to 96.1 of copper. 4 to 13% aluminum with lesser amounts of tinand iron. The use of these comparatively inexpensive alloys has beenseriously handicapped due to their inferior casting properties due totheir high viscosities when molten. I have found that the addition ofmisch metal to such aluminum bronzes in amounts ranging from about 0.2to 5% substantially increases the uidities of the melts to such anextent that they can be cast readily into intricate castings ofexcellent properties.

While I have described what I consider to be the most advantageousmodiiications of my invention it is evident, of course, that variousmodifications can be made in the specific features which have beendescribed without departing from the purview of this invention. My testsshow that the addition of small amounts of one or more rare earth metalsor of misch metal will produce improvemetal containing from about 8 to10% of tin and from more than 50% copper) which are usually classed asbrasses and bronzes. These alloys usually contain at least about 5% ofat least one metal capable of alloying with copper to form a brass orbronze. The more common alloying metals present in this type of alloysare zinc. tiri. nickel, aluminum, manganese, lead, antimony,phosphorous. silicon and cobalt. All castings and alloys of this typeare improved with respect to uniformity of composition. better and moreuniform microcrystalline structure and improved castability due togreater fluidity, these improvements being in addition to specialimprovements, such as elimination of surface inclusions of lead incastings of leaded brasses and bronzes, the elimination of microporosityin certain alloys and improvement in formability in malleable copperalloys, as explained previously. The improvements noted are due to thepresence of the rare earth metals in the misch metal additions. At thepresent time it would not be economically feasible to add these metalsindividually and in pure form to the copper alloys due to theirprohibitive cost in this form. However, should these metals ever becomecommercially available in pure form at moderate cost, the advantages ofthe present invention can be realized by the addition of at least one ofthe rare earth metals to the copper base alloys in proportions rangingfrom .2 to 5% by weight. Other modifications of my invention which fallwithin the scope of the following claims will be immediately evident tothose skilled in the art.

Whatl claim is:

l, An improved process for preventing lead from oozing to the surface ofleaded brass and bronze alloys containing at least 50% copper andbetween about 1 and 35% lead during the casting thereof which comprisesadding from about .2 to 5% of misch metal to such an alloy while in themolten state, and then casting the alloy.

2. An improved process for preventing lead from oozing to the surface ofleaded brass and bronze alloys containing at least 50% copper and atleast 15% lead during the casting thereof which comprises adding about.3% misch metal to such an alloy While it is in the molten state andthen casting the alloy.

3. The process of claim 1 wherein the alloy is an aluminum bronzecontaining from 4 to 13% aluminum.

4. The process of claim l wherein the alloy is a gun metal containingfrom about 8 to 10% of tine and from about 4 to 2% of zinc.

5. The process of claim l wherein the composition of the misch metal isfrom 45 to 55% of cerium, from about 25 to 35% of lanthanum, from about15 to 18% of neodymium with a balance of yttria and further incidentalimpurities, the iron content being less than 1% by weight.

1. AN IMPROVED PROCESS FOR PREVENTING LEAD FROM OOZING TO THE SURFACE OFLEADED BRASS AND BRONZE ALLOYS CONTAINING AT LEAST 50% COPPER ANDBETWEEN ABOUT 1 AND 35% LEAD DURING THE CASTING THEREOF WHICH COMPRISESADDING FROM ABOUT 2 TO 5% OF MISCH METAL TO SUCH AN ALLOY WHILE IN THEMOLTEN STATE, AND THEN CASTING THE ALLOY.